(1) Field of the Invention
The present invention relates to a cartridge for a correction ribbon for typewriters with supply and receiving reels for the ribbon in a container. The receiving reel co-operates with a feed mechanism on the typewriter to feed the ribbon.
(2) Description of the Prior Art
EP-A No. 0 042 955 discloses a cartridge in which the supply reel co-operates with a two-armed spring having a central portion which is of an omega-like shape, making frictional engagement with the hub portion of the reel. One of the two arms has its end fixed to the cartridge and the second arm has an end which co-opertes with the ribbon which is unwound from the reel, with a tensioning function. In each correction cycle the ribbon is caused to advance and the tension of the ribbon causes rotary movement of the second arm, which slightly opens the central part of the spring. The reel is thus free to rotate, permitting the ribbon to unwind. This tensioning device suffers from the disadvantage that, in successive correction cycles, the reel can unwind more turns of ribbon because of the vibration due to the movement of the carriage. In that situation the second arm fails to perform its function of tensioning the ribbon, giving rise to imperfect correction.
EP-A No. 0 021 737 also discloses a tensioning device for a correction ribbon, which provides a toothed ring in the lower part of the supply reel and a slider which is slidable in a guide slot tangentially to the toothed ring and is provided with a pair of teeth capable of engagement with and disengagement from the toothed ring. The slider is spring-loaded in such a way that the feed movement of the ribbon is resisted by the action of the slider on the toothed ring until disengagement of the teeth thereof from the toothed ring. That device is not suitable for use in cartridges for correction ribbons of reduced dimensions.
EP-A No. 0 195 125 discloses a cartridge for a correction ribbon which can be mounted on an oscillating support of the machine. The cartridge is actuated by a feed mechanism which provides a ratchet supported by the container of the cartridge and which normally engages the peripheral teeth on the receiving reel. The ratchet is provided with a control peg which projects from the container and is engaged in a seat of an actuator of the feed mechanism of the machine. In each correction cycle the mechanism is actuated by the oscillating movement of the support for moving the actuator thereof, rotating the reel and thus producing unidirectional feed movement of the correction ribbon. This cartridge is rather complicated. In addition it suffers from the disadvanage that, upon replacement thereof, the operator is required to achieve a high degree of accuracy in positioning the control peg of the ratchet on the seat configuration of the actuator of the feed mechanism of the machine in order to be able to produce correct feed movement of the ribbon in the correction cycles thereof.